Catalytic igniter



Nov. 3, 1964 D. o. NASH ETAL 3,154,920

CATALYTIC IGNITER Filed Nov. so. 1961 United States Patent() 3,154,920 CATALYTIC IGNITER Dudley Gwen Nash and John P. Selmeier, Cincinnati,

Ohio, assignors to General Electric Company, a corporation of N ew York Filed Nov. 30, 1961Ser. No. 156,088 8 Claims. .(Cl. Gil-39.82)

The present invention relates to a combustion initiating and sustaining means for a continuous iiow combustion system, and, more particularly, to a catalytic igniter for use in a high velocity, high temperature, continuous ow combustible gas stream of the type found in aircraft jet engines.

In the continuous ilow combustion systems of the type encountered in turbojet and ramjet combustors, particularly in the thrust augmen-tors, Vor afterburners utilized in the exhaust .ducts of such engines, kit has often proved diilicult rto initiate and sustain combustion, particularly under off-design operating conditions. ratios, for example, combustion is quite often sporadic instead of stable as desired, and at low density, high velocity conditions the flame may kbe easily extinguished due to the combined effects of quenching and low reaction rate. Catalytic igniters have been suggested `as furnishing a possible solution to such problems. However, several additional problems inherent in the design of the prior known catalytic igniters have sometimes prevented utilization of their full potential. It has .been determined that the optimum mechanical design of an igniter should provide a localized surface area for contact with the combustible gas stream while at the saine time avoiding problems connected with thermal shock and mechanical vibration. These problems are interrelated and their solution requires a balance between such factors as: catalytic surface area and weight; gas composition, velocity, and pressure; position of Ithe catalyst within the combustion chamber; the manner in which the catalyst is supported in the gas stream; and any tendency towards oxidation, or burning out of the catalytic igniter element. t

For example, in the high temperature, high velocity combustible gas streams encountered in the .engines of todays supersonic jet aircraft, the problem of extending the life of the igniter means ris particularly acute. The problem has centered around the fact that with known prior art igniter means, as, for example, an igniter such as that shown in Kthe patent to Tecno-2,964,907.- wherein the catalytic element, or screen is positioned within an area of local ilow turbulence caused by a flameholder, or combustion stabilizing device, the .platinum screens have either broken loose or burned outV after short usage due to being in a high Itemperature, high turbulence area. When the catalyst, or igniter element is located within the confines, or immediately downstream of the amehclder, ,temperature variations have proven almost impossible to predict or con-trol. This is detrimental to optimum operation of the combustion initiating and sustaining means sinceV the ctemperature of the igniter itself is critically dependent upon flow of the combustible gas stream through, or around, the catalytic element. Thus, rather 'than utilizing va device wherein the catalytic element fis, in effect, soaking in the turbulent combustion, or flame stabilized zone, it would be desirable to have the igniter directly exposed to the main combustible gas stream.

On the other hand, if the catalytic element `V is exposed to the direct flow of the combustible gas stream, -it will be necessary to provide means whereby thev element is sufficiently protected since otherwise the high velocities and high temperatures associated with the gas streams A t low fuel-air 3,154,920 Patented N ov. 3, 1964 ice in supersonic V,jet engines, for example, may cause the element to break cr rupture and Vbe ejected kfrom the jet engine exhaust pipe after a relativelyshort period of operation. Thus, `there is an additional requirement to reduce, or control the pressure load on the Acatalytic element. At the same time, there cannot be created any serious ignition delay, or otherwise the ,combustion .ini- Itiating and sustaining Vmeans would not perform its function in an optimum manner. Therefore, adoption of such an arrangement presents difficulties in determining where the catalytic element should best be `placed for optimum operation, including the design -0.f .the means whereby the element will Vbe Supported and maintained in the Ahigh velocity, high temperature combustible gas stream for optimum life.

Accordingly, an object of the present invention is ,to provide a `more .eicient combustion initiating and sustaining means Vfor use `in a high velocity, high temperature, continuous flow combustion system.4

A `further .object of the invention is Vto `provide an improved, .more ,eihcient catalytic igniter for use in :a continuous llow, high temperature, high velocity combustible gas stream of the type -found in Va turbojet or ramjet engine.

Astill further `object of .the present invention is to provide Va more efficient catalytic igniter for use in acontinuous flow vcombustion system, the igniter being so located as to ,provide improved igniter temperature control and ,fast ignition `response while at the Sametime increasing the useful operating life of the igniter.

In carrying out the .aforementioned objects, a preferred embodiment of the invention `comprises an igniter means including a supporting member adapted to contain a catalytic element, the element lbeing prevented from contacting thev ,supporting member by vmeans -of a refractory material, the supporting member being mounted on a flameholder inserted in a -high velocity, continuous flow combustible gas stream in a manner such Ithat ,the catalytic .element is located outside 'the region of `local turbulence caused by introduction of sa ame stabilizing device in the combustible gas stream with a cooling gas lil-m being provided between the supporting member andthe flameholder.

The features of rvthe invention which are believed to be novel are set ,forth .with :particularity inthe appended claims. The invention itself, however, both as to lits organization and'operation, together withfurther lobjects and advantages thereof, may `best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGURE 1 is a side elevation view of a jet engine exhaust .pipe in which is mountedgafterburning,` or thrust augmentation combustion apparatus in combination with the `improved igniter means oflthe subject invention;

FIGURE 2 is an :enlarged pictorial Vview of the `irn- ,proved combustion initiating and sustaining means of ,the subject invention; t

FIGURE 3 is a fragmentary View partially in cross section taken along. line 3-- 3 of FIGURE 2;

FIGURE 4 :is a fragmentary, exploded View, partially in cross section, illustrating the relative placement of the catalytic lelement in the igniter means;

FIGURE 5 lis a view taken along line 5-5 of FIG- URE 2; and f a FIGURES 6r and 7 are illustrations of further embodiments of the subject invention. i p

While lignition in a jet engine afterburner section, in

particular, can be Vaccomplished by use of pilot burners, or the sofcalled hot streak systems, these -reqiure sep-vr arate-fuel supplies, and associated equipmehand often y vThese and vadditionalfa'ctors, as A special air supplies.

3,1 3 stated above, have lead to the suggested use of catalytic igniters. However, as pointed out, the prior art igniters have had a number of development problems connected therewith, which the present invention, now to be more fully described, is believed to have overcome.

In FIGURE 1 there is depicted schematically a jet engine tailpipe, or exhaust duct having an outer casing, or shell 10. The tailpipe may include an annular center body 14 which divides the exhaust area into an annulus through which flows the stream of hot combustible gases, indicated by the solid arrows, exiting from the engine turbine section (not shown) upstream thereof. As in most afterburning, or thrust augmentation systems, a fuel injector 16 is provided which projects transversely of the combustile gas stream. It is also common to use a flame stabilizing device, or ameholder inserted in the combustible gas stream downstream of the fuel injection means. taken the form of V-shaped, annular gutter members, such as those indicated by numeral 18, in FIGURE 1. Indicated generally at 20, in FIGURES 1 and 2, is the improved combustion initiating and sustaining means which comprises the subject of the present invention.

Referring now specifically to FIGURE 2, where the invention is shown in greater detail, it will be seen that the improved igniter means includes a support member indicated generally at 22. The support member illustrated has a pair of L.shaped mounted portions 24-24 extending outwardly of a connecting body portion, or frame 26. The body portion, or frame is adapted to be supported by means of the L-shaped mounting, or leg portions on bracket means 28 attached to the upstream portion 29 of the generally V-shaped flamerholder by means' of suitable fastening means, such as bolts 30. It will be seen from the drawing that the flameholder includes a pair of spaced,

or diverging wall portions 31-31 which create a stabilized, or turbulent flame zone therebetween when introduced into the main combustible gas stream. This facilitates localized burning in a well-known manner. As seen perhaps more clearly in FIGURES 3 and 4, the body portion, or frame of the support member 22 is 'folded over at 32 so as to create a hollow, or cavity 34. The front wall 35 of the body portion includes a single enlarged aperture 36 facing in the downstream direction. On the other hand, the rear wall 37 of the -body portion includes a multipicity of relatively small apertures 38, as may best be seen in FIGURE 5.

Adapted to be located within the hollow portion, or cavity 34 of the body 26 is a retainer member in the form of a plate 40. Immediately behind, or upstream of the plate is located the catalyst. In this embodiment -the catalyst is in the form of a platinum, or a platinum containing alloy element 42. As shown, the element consists of a fine wire mesh, or screen which is held in place by the retainer plate 40. It `will be noted from FIGURE 2, in particular, that the retainer plate includes a plurality of openings 44 which permit combustible gases entering the cavity 34 from the upstream holes 3S, in the body wall 37, to flow therethrough and out the enlarged aperture 36. .The platinum wire mesh is, of course, air permeable, the size of the openings in the screen being controlled so as to permit a desired rate of ow, in cooperation with the sizing and arrangement of the openings 38 and 44 in the wall 37 and plate 40, respectively.

One of the features of the present invention is means whereby the operative life of the platinum wire screen, catalytic element is prolonged. It has been found that the useful life of the element improves as thev flow of .the combustible gas stream through the igniter is reduced since a reduced flow-will result in a reduction of both the heat generated and the pressure load on the screen.

catalytic element `to reach Ythe steady state temperatures desired for optimum combustion initiation and Typically, these flame stabilizing devices have sustention. The invention therefore embodies a feature whereby serious ignition delays can be avoided by means of providing an insulating means in the form of a refractory material between the platinum screen, or mesh 42 and the support, or holder 22, and between the mesh and the retainer or support plate 40. This reduces the heat loss from the screen caused by conduction to the retainer plate or to the holder. Thus, a refractory material is interspersed between the plate and the inner walls of the cavity 34 which serves as an insulator to reduce heat loss from either the catalytic element or the retainer plate, should it be desirable not to insulate the latter, e.g., if it also were to contain platinum, or a similar catalytic material. A further benefit of coating, for example, a ceramic material on the plate and/or the screen is that destruction of the igniter element due to the formation of low melting point alloys resulting from direct contact between the plate or screen and the support member 22 will be prevented. In other words, problems inherent in catalytic gniters wherein the catalytic element itself is in contact with the support means in an atmosphere such as to enhance the creation of metallurgical interaction or oxidation of the support means in the presence of the platinum, or platinum containing alloy element, are eliminated with use of the present invention which insulates the catalytic element from the support means. Thus, the use of the refractory material enables the catalytic igniter means to be located in a very high temperature combustible gas stream in such a manner as to increase the igniters comubustion initiation and sustention properties without danger of burning out or destruction of the retaining, or support means, or loss of the catalytic element.

This leads to another primary feature of our invention, namely, the mounting arrangement. As has been pointed out, the effectiveness and reliability of any igniter element and, in particular, an igniter utilizing a catalytic element, depends primarily on control of the temperature in the area of exposure of the igniter to the combustible gas iiow. Accordingly, in contrast to the prior lart continuous combustion flow devices wherein the cat- 'and number of the holes 38 in the upstream portion of the supporting means, as well as the size, or combined area, of the holes in the downstream supporting, or retaining means 40, the rate of flow can be adjusted for a variety of iiow conditions in any engine application. However, in the type of high velocity, high pressure continuous combustible gas stream found in supersonic jet engines an unusually rigid support means may be required. It has also been found that the method of mounting the igniter within the gas stream, on the flameholder, is also critical. Referring therefore to FIG- URES 2 and 7, it will be noted that the brackets 28 are channel-'shaped so as to provide an opening 52 at the upstream edge of the flameholder 18. The opening S2 is in the form of la slot leading to a. channel or passageway S4 formed between one of the V-gutter walls 31 and an L-shaped extension, or leg 24 of the support member 22. In operation, the combustible gas stream which is relatively cool upstream of the frameholder compared to that downstream thereof, enters the open back of the brackets 28 passing through the opening SZ and is directed along the oppositely facing surfaces bf the flameholder and the support member legs, exiting at 56 adjacent the downstream edge of the ilameholder wall 31.'.'' In effect, the

described arrangement provides a cooling film over the surface of the suporting means and the wall 31, thus enhancing the life of the igniter means and flameholder wall, since the possibility of destruction due to overtemperature is minimized.

As seen in FIGURE 6 in an alternate embodiment, the body portion of the support member is modified, or simplied, by elimination of the upstream wall 37. In its place a sintered metallic screen 50 is utilized. The screen may be coated with a ceramic, or other refractory material in the same manner as is the inner wall of the cavity 34. In addition, the use of the sintered screen provides a large multiplicity of openings through which the com bustible gas stream may impinge on the catalytic element. It would be possible in a iow stream of sufficiently reduced velocity to support the catalytic element between a pair of sintered metallic screen members 50, suitably attached to a support means similar to the frame portion 26, shown in the present embodiment. It is therefore understood that it is our intention to cover as well other modifications of supporting means obviously within the teachings of the invention as occur to those skilled in the art.

A further embodiment of the invention comprises the addition of a bafile member 58, as seen in FIGURE 7. In this embodiment, the bafe is in the form of a rectangular skirt attached at the downstream edge of the body portion. With this arrangement, the flameholding capability of the igniter means is improved by the baffle or skirt overlapping the spaced ameholder walls 31-31 which minimizes any problem connected with ignition of the fiameholder in the presence of the cooling ow exiting at 56.

While the present invention has been described in connection with a turbojet or ramjet afterburner it also has application to a main combustion system for use in a gas turbine type engine. In such an application, the improved combustion ignition and sustaining means, including the supporting and insulating arrangement described herein, will be located so as to enhance the transfer of heat from the ignition means to the combustible gas stream to facilitate ignition.

Obviously, other modifications and variations of the present invention will be possible in the light of the above teachings. It is therefore understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described, including the alternate embodiments thereof.

What is claimed is:

1. In a high velocity, continuous flow, combustible gas stream:

a ameholder having spaced walls creating a region of local flow turbulence therebetween;

a support member including a hollow, generally rectangular body portion arranged at right angles to the gas stream and having an opening therein permitting the flow of combustible gases therethrough, and at least one leg portion extending from said body portion;

ignition means retained in said body portion, said ignition means comprising a flowpermeable catalytic element;

refractory material interspersed between the catalytic element and the body portion to prevent contact therebetween;

and means attaching said support member to the flameholder so that said body portion is outside the region of local turbulence and a stream of cooling gases ows between the support member and the flameholder.

2. In a high velocity, continuous flow combustible gas stream:

a ameholder having spaced walls creating a region of local iiow turbulence therebetween;

a support member including a hollow, generally rectangular body portion arranged at right angles to the gas stream and having an opening therein permitting the flow of combustible gases therethrough and mounting means extending therefrom;

retainer means in said body portion;

ignition means in said body portion, said ignition means being in abutment with and supported by said retainer means and comprising a flow-permeable catalytic element;

refractory material interspersed between the retainer means and the body portion in a manner such as to prevent direct contact between the body portion and the catalytic element;

and means attaching said support member mounting means to the flameholder so that said body portion is outside the region of local turbulence and a cooling gas stream is directed to flow between said mounting means and said flameholder.

3. The apparatus as claimed in claim 2 wherein said catalytic element comprises a platinum alloy wire mesh.

4. The apparatus as claimed in claim 2 wherein said retainer means includes a plate of platinum and a sintered metallic screen, said plate and screen being located downstream and upstream of said element, respectively.

5. The apparatus as claimed in claim 4 wherein said refractory material comprises a ceramic coating applied to said retainer means.

6. In a high velocity, continuous flow, combustible gas stream:

a flameholder having spaced walls creating a region of local flow turbulence therebetween;

a support member including a hollow generally rectangular body portion and a mounting portion, said body portion having openings in upstream and downstream walls thereof and said mounting portion includes a leg extending `from each of a pair of opposite sides of said body portion;

ignition means in said body portion, said ignition means comprising a gas permeable catalytic element;

refractory material in said body portion, said material being interspersed between the element and the support member to prevent contact therebetween;

and means attaching said support member mounting portion to the ameholder including at least one bracket member aliiXed to the flameholder, and means for fastening one of said legs to said bracket member,

said bracket member having an opening therethrough leading to an auxiliary passage bounded on one side by said one leg of said mounting portion and on an opposite side by one of said ilameholder walls, said auxiliary passage accepting a portion of the gas stream flow upstream of said flameholder and providing a cooling gas film for said support member mounting portion.

7. The apparat-us claimed in claim 6 wherein the body portion includes means diverting the flow of cooling gases exiting from said auxiliary flow passage towards the region of local turbulence.

8. The apparatus claimed in claim 7 wherein the ow diverting means comprises a baie member affixed to said hollow, generally rectangular body portion on the downstream'side thereof.

References Cited in the tile of this patent UNITED STATES PATENTS 2,929,211 Meyer et al. Mar. 22, 1960 2,941,361 Spalding June 2l, 1960 2,964,907 Toone Dec. 20, 1960 2,970,439 Berl Feb. 7, 1961 2,972,227 Allen Feb. 2l, 1961 

1. IN A HIGH VELOCITY, CONTINUOUS FLOW, COMBUSTIBLE GAS STREAM: A FLAMEHOLDER HAVING SPACED WALLS CREATING A REGION OF LOCAL FLOW TURBULENCE THEREBETWEEN; A SUPPORT MEMBER INCLUDING A HOLLOW, GENERALLY RECTANGULAR BODY PORTION ARRANGED AT RIGHT ANGLES TO THE GAS STREAM AND HAVING AN OPENING THEREIN PERMITTING THE FLOW OF COMBUSTIBLE GASES THERETHROUGH, AND AT LEAST ONE LEG PORTION EXTENDING FROM SAID BODY PORTION; IGNITION MEANS RETAINED IN SAID BODY PORTION, SAID IGNITION MEANS COMPRISING A FLOW-PERMEABLE CATALYTIC ELEMENT; REFRACTORY MATERIAL INTERSPERSED BETWEEN THE CATALYTIC ELEMENT AND THE BODY PORTION TO PREVENT CONTACT THEREBETWEEN; AND MEANS ATTACHING SAID SUPPORT MEMBER TO THE FLAMEHOLDER SO THAT SAID BODY PORTION IS OUTSIDE THE REGION OF LOCAL TURBULENCE AND A STREAM OF COOLING GASES FLOWS BETWEEN THE SUPPORT MEMBER AND THE FLAMEHOLDER. 